The Atomics International "Aqueous Carbonate Process" employs a spray dryer assembly to remove SO.sub.x from flue gases. In this process, an aqueous solution of sodium carbonate is sprayed at low 1/g ratios into the spray dryer through which flue gases containing fly ash are passed. The SO.sub.x reacts with the Na.sub.2 CO.sub.3 to form Na.sub.2 SO.sub.3 and Na.sub.2 SO.sub.4 while the heat dries the droplets to powder form. The powdered Na.sub.2 SO.sub.3, Na.sub.2 SO.sub.4 and fly ash is then collected in a cyclone and electrostatic precipitator downstream before the cleaned flue gas is exhausted to the atmosphere.
This process is a single-stage SO.sub.x removal process, and employs two types of particulates clean-up apparatus: the cyclone portion of the spray dryer and an electrostatic precipitator. Both clean-up units are downstream of the aqueous spray dryer reactor which receives the full gas volume containing both fly ash and SO.sub.x without pretreatment. The grain loading for the cyclone and electrostatic precipitator is much higher than usual, i.e., fly ash alone, because of the added Na.sub.2 SO.sub.3 and Na.sub.2 SO.sub.4. As a consequence, some sulfites and sulfates can blow by these devices and be exhausted to the atmosphere. The SO.sub.x removal efficiency is entirely dependent on control conditions in the spray dryer apparatus which acts both as a reactor and a dryer, and in part also acts as a collector.